Continuously tunable lasers are well-established and are commonplace in telecommunications applications. Although telecommunications lasers operate to fixed grids (eg ITU grids), tunable lasers need to be set up for a variety of applications and some extent of wavelength tunability is desirable to allow for correction of wavelength drift as the laser ages. Unfortunately, the requirement for full range continuous tunability results in expensive and power-hungry electronic circuitry, most particularly due to the requirement for digital-analog conversion (DAC) chips.
Distributed Feedback (DFB) lasers in which the gratings are built into the gain medium are being replaced by Distributed Bragg Reflector (DBR) lasers, particularly where tunability is required. For a wide range of tunability a Sampled Grating (SG) DBR laser is one typical option. In such a laser, the grating (often referred to as a “comb grating”) gives rise to a comb of reflectivity peaks which can be tuned to select the required lasing wavelength.
In an alternative design of tunable laser, Digital Supermode DBRs (DS-DBRs) may be utilised. The DS-DBR design has the advantage over SG-DBR in that no DACs are required. However, tunable lasers made entirely on semiconductor chips have been impossible without gratings requiring DACs for control. For example, no tunable laser has been made with solely DS-DBR gratings (i.e. no other types of gratings). The challenge of this patent application is to create tunable lasers based upon the DS-DBR design principle but with cheaper and lower power consuming control electronics, in particular not requiring DACs. Semiconductor lasers, made absent DACs for primary control, are disclosed herein. This is achieved principally by devising finite state tunable devices.
The application of the AWG as a wavelength selective device for laser arrays is known (Keyvaninia et al, Optics Express, 21 (No 11) p 13675, 30 May 2013).